1. Field of the Invention
This invention relates to a fluid for a traction drive (rolling friction drive device), and more specifically, to a traction drive fluid which has a high traction coefficient and excellent stability to heat and oxidation and is economically advantageous.
1. Description of the Prior Art
In traction drive transmissions, it is required that the traction fluid lose its fluidity by entering a rolling contact point to form a film thereof, at which contact point two cylinders or cones rolling in the directions opposite to each other about their respective fixed rotation axes contact each other at the surface, and that the traction fluid recover its original fluidity on leaving the contact point. In other words, the traction fluid desirably exhibits high rolling friction in use since power is transmitted by means of rolling friction caused by hardening of the film of the traction fluid (the traction fluid in filmy state at high pressures) at the rolling contact point in the traction drive transmissions. The rolling friction property required of a traction fluid is expressed by a rolling friction coefficient measured in a predetermined traction drive transmission.
Various compounds have heretofore been proposed as fluids for traction drives. They include, for example, decalin, perhydroanthracene (U.S. Pat. No. 3,411,369), polycyclohexyls (U.S. Pat. No. 3,925,217), 2,3-dicyclohexylbutanes (Japanese Laid-Open Patent Publication No. 4510/1971), a hydrogenation product of an isobutylene low polymer (Japanese Laid-Open Patent Publications Nos. 4766/1971, 2164/1972, 35661/1972 and 2229/1972), a hydrogenation product of a cyclic dimer of alpha-methylstyrene (Japanese Laid-Open Patent Publication No. 2229/1972 and Japanese Patent Publication No. 35763/1972), a hydrogenation product of a linear dimer of alpha-methylstyrene (Japanese Laid-Open Patent Publication No. 7664/1972 and U.S. Pat. Nos. 3,975,278 and 3,994,816), and adamantanes (Japanese Patent Publications Nos. 42067/1973, 42068/1973 and 35763/1972). Many of these compounds are insufficient in practical properties, particularly a rolling friction coefficient, i.e. a traction coefficient. Some of these compounds such as the linear dimer of alpha-methylstyrene, have satisfactory practical properties, but are not economically advantageous because the starting materials for their production are expensive or the occurrence of side-reactions during their production decrease the yields of the desired products.